1. Field of the Invention
This invention relates to a mercury-rare gas discharge lamp, and more particularly to a mercury-rare gas discharge lamp which is suitable for use in the printing or copying of patterns of ICs, LSIs and ultra LSIs.
2. Description of the Prior Art
The recent development of ultra LSIs requires printing or copying techniques with tolerances of less than 1 micron.
In the prior art, printing or copying techniques with tolerances of 1 micron or more are already in practice, employing a discharge lamp emitting ultraviolet rays of wave-lengths in the range of 3500 to 4500 A and a photoresist sensitive to the ultraviolet rays of these particular wave-lengths. But the prior art method cannot be used to achieve tolerances of less than 1 micron due to interference. For such tolerances electron beam lithography and X-ray lithography techniques have been studied and developed rapidly to take the place of the discharge lamp. These techniques, used in combination with a computer, permit of automation and simplification of the printing or copying process on one hand, but these have a fatal defect of requiring too much time for exposure on the other hand, and hence are said to be of little practical utility.
This led to a restudy of the combined use of a discharge lamp and a photo resist for utltraviolet rays to obtain a photoresist sensitive to ultraviolet rays having wave lengths less than 3000 A and a discharge lamp emitting such ultraviolet rays in large quantities.
Fortunately, it was ascertained by experiments in 1974 that a photoresist PMMA for use with electron beams could be sensitized by ultraviolet rays of wavelengths less than 2000 A (Applied Physics Letters, Vol. 25, page 451), and in 1975 that the photo resist PMMA could also be utilized for copying with rays of wavelengths between 2000 to 2600 A (J. Vac. Sci. Technol., Vol. 12, page 1317). As a result of this, the problem remaining to be solved is to obtain a discharge lamp which is capable of emitting a sufficient quantity of ultraviolet rays of wavelengths less than 3000 A.